High pressure discharge lamp of the cooled electrode type

ABSTRACT

A high pressure discharge lamp of the cooled electrode type comprising electrodes, an envelope sealing portion for said electrodes and said envelope, and a cooling liquid inlet passage and a cooling liquid outlet passage formed in the interior of at least one of said electrodes for introducing a cooling liquid into same discharging same therefrom. An indented or grooved portion and bulkheads are provided so as to form a snaky cooling liquid passage in the interior of the forward end portion of said electrode for increasing the area for dissipating heat from the electrode and for increasing mechanical strength of the forward end portion of said electrode.

United States Patent [72] Inventors Yasuhiro Shimizu;

Yoshihiko Nakamura, both of l-limeji, Japan 21 Appl, No. 837,294

[22] Filed June 27, I969 [45] Patented Sept. 14, 1971 [73] AssigneeUshio Electric Inc.

Tokyo, Japan [32] Priority July 1, 1968 [54] HIGH PRESSURE DISCHARGELAMP OF THE COOLED ELECTRODE TYPE 1 Claim, 16 Drawing Figs.

[52] US. Cl t. 313/32, 313/ 184 [51] 1nt.Cl H0lj 61/52 [50] Field ofSearch 313/30, 32,

[56] References Cited UNITED STATES PATENTS 3,474,278 10/1969 Thouret eta]. 313/30 X 3,521,103 7/1970 Nakamura et a1.

Primary Examiner-Roy Lake Assistant Examiner-Palmer C. DemeoAttorney-Stevens, Davis, Miller & Mosher ABSTRACT: A high pressuredischarge lamp of the cooled electrode type comprising electrodes, anenvelope sealing portion for said electrodes and said envelope, and acooling liquid inlet passage and a cooling liquid outlet passage formedin the interior of at least one of said electrodes for introducing acooling liquid into same discharging same therefrom. An indented orgrooved portion and bulkheads are provided so as to form a snaky coolingliquid passage in the interior of the forward end portion of saidelectrode for increasing the area for dissipating heat from theelectrode and for increasing mechanical strength of the forward endportion of said electrode.

PATENIED SEP 1 4 m: 3 -504 95 Ana/P H PATENTED SEP14lB7I sum 2 or 3 HIGHPRESSURE DISCHARGE LAMP OF THE COOLED ELECTRODE TYPE The presentinvention relates to high pressure discharge lamps, and in particular toa high pressure discharge lamp of the cooled electrode type.

Carbon arc lamps have hitherto been employed in solar simulators forspace development used for carrying out tests on the irradiation of sunsrays in the outer space where a vacuum prevails or in arc image furnacesused for the study of materials resistant to super high temperatureswhich are apparatus for melting heat resistant substances by opticallyconcentrating radiating rays or heat rays of discharge lamps. Carbon arclamps have the disadvantage of being consumed in several to scores ofminutes and require replacements each time they are consumed. Moreover,the position of arcs always shifts, so that carbon arcs have been veryinconvenient to handle. Accordingly, small type short arc high pressuredischarge lamps which contain mercury or a rare gas, such as xenon,argon or the like, enclosed in an envelope under high pressure havegradually taken the place of carbon arc lamps and come to be favoredbecause of their convenience of handling and the stability of theirarcs. As the equipment grows larger in dimensions, a demand for adischarge lamps of higher output has greatly increased in recent years;and air cooled Xenon short are discharge lamps having a maximum capacityfor 8 kw. and capable of being in service for several hundred hours havebeen developed up to the present. There is a growing demand for largetype discharge lamps with a capacity for 20, 30, 50 or higher kw.

Short arc discharge lamps of the type described are not withoutdisadvantages. For example, short are discharge lamps containing xenonor other rare gas enclosed in the envelope which as the largest demandhave a low potential gradient at an operating pressure of 20 to 30atmospheres, so that the lamp voltage does not rise above about 60 v. inthe short discharge distance of within about mm. If the voltage isforcibly raised above that level, there will be the danger of explosionof the lamp. This makes it necessary to use a low voltage and a currentof high value when it is desired to apply a power of high value. Whenthe capacity of the lamp is, say, kw. and the distance between theelectrodes is about 12 mm., the proper lamp current and voltage will beone of 400 to 500 A, 50 to 40 v. In the rare gas under high pressure,the are generated by such current will have a diameter limited to about10 mm., and when the current is a DC current there will occur a heatloss corresponding to a current of high value up to several kw. in asmall portion with a diameter of about 10 mm. disposed at the forwardend of the anode. The anode tends to melt at temperatures above about200 A and evaporate at elevated temperatures even when the anode isformed of tungsten which has excellent thermal and electric conductivityand the highest resistance to heat of all the pure metals. It has thusbeen difficult to produce high pressure short are discharge lamps havinga long practical service life.

Accordingly, the principal object of the present invention is to providea high pressure discharge lamp of the cooled electrode type in which theforward end of at least one of the electrodes is cooled with a liquidfor preventing melting and evaporation.

Another object of the invention is to provide a high pressure dischargelamp of the cooled electrode type in which indentations or openings areformed on the walls in the interior of the forward end of the electrodewhich is brought into contact with a cooling liquid so as to cause thecooling liquid to flow in a zigzag direction and to increase the heatdissipation area of the electrode.

This invention consists in the provision of a high pressure dischargelamp of the cooled electrode type comprising electrodes, an envelope,sealing portions for said electrodes and said envelope, a cooling liquidinlet passage and a cooling liquid outlet passage formed in the interiorof at least one of LII said electrodes for introducing a cooling liquidinto the forward end portion of said electrode and discharging sametherefrom, an indented or grooved portion provided in the interior ofthe forward end portion of said electrode for increasing the area fordissipating heat from the electrode and for increasing mechanicalstrength of the forward end portion of said electrode, a main bulkheadprovided at right angles to the longitudinal direction of the indentedor grooved portion along the axis of said electrode, said main bulkheadbeing connected to the convex surfaces of the indented or groovedportion, sub-bulkheads provided at the both sides of the main bulkhead,and sub-bulkheads being connected to the convex surfaces of the indentedor grooved portion in the longitudinal direction thereof, these mainbulkhead and sub-bulkheads forming together a snaky cooling liquidpassage.

Other objects and advantages of this invention will become apparent fromconsideration of the following description when taken in conjunctionwith the accompanying drawings, in which:

FIG. 1A is a longitudinal sectional view of a conventional high pressuredischarge lamp of the cooled electrode type showing its bulb portion;

FIG. 1B is a view in section taken on the line II of FIG. 1A;

FIG. 2A is a longitudinal sectional view of another conventional highpressure discharge lamp of the cooled electrode type showing its bulbsection;

FIG. 2B is a view in section taken on the line IIII of FIG. 2A;

FIG. 3 is a longitudinal sectional view of a further conventional highpressure discharge lamp of the cooled electrode type showing its bulbsection;

FIG. 4 is a detailed sectional view of the anode portion of theembodiment shown in FIG. 3;

FIG. 5 is a view in section taken on the line V-V of FIG. 4;

FIG. 6A is a longitudinal sectional front view of one embodiment of thepresent invention;

FIG. 6B is a longitudinal sectional side view of the embodiment shown inFIG. 6A;

FIG. 7 is a detailed sectional view of the anode portion of theembodiment shown in FIGS. 6A and 68;

FIG. 8 is a view in section taken on the line VIlIVlll of FIG. 7;

FIG. 9 is a view in section taken on the line IX-IX of FIG.

FIG. 10 is a view in section taken on the line X-X of FIG.

FIG. 11 is a view in section taken on the line XI-XI of FIG.

FIG. 12 is a view in section taken on the line XII-XII of FIG. 7;

FIG. 13 is a view in explanation of the principal part of the highpressure discharge lamp of the cooled electrode type according to thisinvention.

FIGS. 1A, 18, 2A and 2B are views in explanation of conventional highpressure discharge lamps of the cooled electrode type. 1 is an envelopeformed of quartz; 2 and 3 are an anode and a cathode respectivelydisposed in face to face relation in the envelope 1 formed of quartz; 4aand 4b are cooling liquid inlet tubes inserted in the interior of theanode 2 and the cathode 3 respectively; 5a and 5b are cooling liquidoutlet passages formed between the outer wall of said inlet tube 4a andthe inner wall of said anode 2 and the outer wall of the inlet tube 4band the inner wall of the cathode 3 respectively; and 6 is a coolingliquid discharge port formed in the center of the forward end of saidcooling liquid inlet tube 4a, the arrows indicating the direction offlow of the cooling liquid. In this type of discharge lamps, the coolingwater flows along the inner surface of the forward end of the anode 2and is led into the outlet passage 50 through the center of the forwardend of the anode.

It has been found that various problems on materials have to be solvedwhen it is desired to increase the value of a current to be applied tolamps of the type described. Each material has its own natural thermalconductivity, and the maximum temperature to which the heat generatingportion of an electrode is subjected should be below the melting pointtemperature of its material. The rate of evaporation and deposition ofthe materials for electrodes in the period of several hundred hoursduring which the lamps are kept in service vary depending on thematerials. When, for example, the vapor pressure of the materials forelectrodes is held below about l to torr in order to obtain a desiredrate of evaporation and deposition, it is required to maintain themaximum operating temperatures of the electrode T to a level which isdetermined by the material used. If the boundary temperature Tw of thecooling side is maintained by means of a cooling liquid at, say, 100 C,there is a maximum value Q in the amount of heat which can be made topass through the forward end of the electrode in a unit hour if the areathereof is kept constant. The maximum value of heat Q can be expressedfor the formula =kslt (T,,,,,,-Tw) wherein t is the thickness of theforward end of the electrode, s is the area of the forward end of theelectrode, and A is the thermal conductivity of the electrode.

if the materials used and the pressure in the lamp between theelectrodes were maintained constant, it would be impossible to increaseQ,,,,, unless the thickness t of the forward end of the electrodes ismade smaller, since A, s and T inherent in each material of theelectrodes are constant. The forward end of the electrodes, be theyformed of copper, tungsten or molybdenum, should be below about 3 mm, inthickness when the current used is in the order to kw. and 400 A, ifmelting or evaporation of the electrodes is to be prevented. One of theconditions that has to be satisfied by all means if the electrodes areto be made to withstand a current of higher values would be to make thethickness of the forward end of the electrodes as small as possiblebelow 3 mm.

To sum up, various conditions are set forth above combine to make itdifficult to obtain a practicable discharge lamp having a high inputwhich is free from the danger of deformation or evaporation of theelectrodes if a conventional simple two dimensional construction isused.

On the other hand, the surface of the electrodes of a high pressuredischarge lamp tends to undergo a deformation due to a very highpressure of gas of scores of atmospheres in the discharge space and adegradation of the mechanical strength of the material caused by a risein the temperature of the forward end of the electrodes while the lampis lighted. This has set allowable minimum thickness for materials usedfor preparing the liquid cooled electrodes of conventional twodimensional construction. It has thus been quite difficult to obtain apracticable liquid cooled high pressure discharge lamp that can operatein a stable manner with a current of over 400 A (over 15 to 20 kw.),even if copper, tungsten or molybdenum is used as a material forpreparing the electrodes.

Even if the anode 2 and the cathode 3 of a discharge lamp are cooleddirectly with a liquid, the current passing through the electrodes willhave a high density characteristic of light sources when the lamp is ofhigh voltage and high luminance. Particularly, the area with a diameterof several millimeters in the center of the anode 2 is raised to a veryhigh temperature. It is thus required to increase thermal conductivityof the anode 2, reduce the thickness of the anode 2 as much as ispossible without decreasing mechanical strength, and make the coolingwater remove heat from the anode 2 which is heated to a very hightemperature, in order that melting or evaporation of the material ofanode 2 which generates an arc may be prevented. in conventionaldischarge lamps, however, the rate of flow of a cooling liquid passingthrough the center portion of the anode has a tendency to slow downbecause of the arrangement in which the cooling water discharge port 6of the anode cooling liquid inlet tube 40 is disposed in the center ofthe inner wall of the forward end of the anode 2, thereby reducingthermal conductivity. Moreover, the cooling liquid has a tendency toboil when passing through this portion because of the high heatgenerated therein, thereby further reducing thermal conductivity of theelectrode. Accordingly, the anode 2 has tendency to evaporate under arelatively low current density, with the result that the discharge lampis darkened and its service life is shortened.

The aforementioned disadvantages can be obviated by arranging as shownin FIGS. 2A and 23 that the discharge port 6 of the cooling water inlettube 4a inserted in the anode 2 is disposed on one side of the front endportion of the anode, so that the cooling liquid can flow along theinner surface of the front end portion of the anode 2 into the coolingliquid outlet passage 5a. This arrangement is conductive to preventingthe slow down of the flow of cooling liquid in the center of the forwardend portion of the anode 2 and boiling of the cooling liquid in thisportion of the anode, so that the cooling liquid can effectively performthe function of continuously cooling the center of the front end portionof the anode. ln embodiments shown in FIGS. 3 to 5, there is provided anindented or grooved portion 7 in which a number of indentations orgrooves extending parallel to one another transversely of the anode areformed on the walls in the interior of the front end portion of theanode 2 cooled by a cooling liquid, one end of said indented portion 7being connected to a cooling liquid inlet passage 8 and the other end ofthe indented portion 7 being connected to a cooling liquid outletpassage 9. The cooling liquid inlet passage 8 and outlet passage 9 aredefined by the walls of the electrode and a partition 10 mounted axiallyin the center of the electrode. In high pressure discharge lamps havingthe above-mentioned structure, the area for dissipating heat increases,but the distance of the indented or grooved portion 7 heated to a hightemperature through which the cooled water passes is short. Thesectional area may be made large by increasing the number ofindentations or grooves in the indented or grooved portion 7 in order toobtain the large output. However it is difficult to manufacture highpressure discharge lamps having such a structure.

The present invention has been made to provide improvements in highpressure discharge lamps of the cooled electrode type. The inventionwill now be explained with reference to embodiments illustrated in FIGS.6 to 13. In the high pressure discharge lamps of this invention, anindented or grooved portion 7 in which a number of indentations orgrooves extending parallel to one another transversely of the anode areformed on the walls in the interior of the front end portion of theanode 2. Connected to the convex surfaces of the indented or groovedportion 7 is a main bulkhead 11 at right angles to the longitudinaldirection of the indented or grooved portion 7 and along the axis of theanode 2.

At both sides of the main bulkhead 11 are provided subbulkheads 12, 12connected to the convex surfaces of the indented or grooved portion 7 inthe longitudinal direction thereof. These main bulkhead 11 andsub-bulkheads l2, 12 form together a snaky cooling liquid passage asindicated by arrows in FIG. 10, one end of said passage being connectedto a cooling liquid inlet passage 8 and the other end of said passagebeing connected to a cooling liquid outlet passage 9 respectively.

Except for said cooling liquid inlet passage portion and said coolingliquid outlet passage portion within said anode 2, the other portionswhich are surrounded with the main bulkhead 11, the sub-bulkheads l2, l2and the inside wall of the anode 2 are covered by covering plates 14,respectively so as to provide spaces 13 of suitable size therein.

It will be appreciated from the foregoing description that thedistribution of the flow of the cooling liquid in the center of theforward end portion of the anode 2 of a discharge lamp according to thisinvention becomes more constant and therefore an excellent coolingfunction can be obtained, compared with the conventional discharge lampsin which only indented or grooved portions are formed.

Further, since the passage for the cooling water in the for ward endportion of a high temperature of the anode 2 is several times as long asthat of prior art discharge lamp, the amount of the cooling water ismarkedly reduced. It will thus be appreciatedthat the present inventionpermits to an increase in the maximum allowable current of one and halftimes as much as that of the conventional high pressure discharge lamps.

It should be understood that the specific preferred embodiment andpractices which have been depicted and described herein have beenpresented by way of disclosure rather than limitation, and that thoseskilled in the art will appreciate that various modifications,combinations and substitutions may be effected without departure fromthe spirit and scope of this invention in its broader aspects and as setforth in the accompanying claims.

What is claimed is:

l. A high pressure discharge lamp of the cooled electrode typecomprising electrodes, an envelope, sealing portions for said electrodesand said envelope, a cooling liquid inlet passage and a cooling liquidoutlet passage formed in the interior of at least one of said electrodesfor introducing a cooling liquid into the forward end portion of saidelectrode and discharging same therefrom, an indented or grooved portionprovided in the interior of the forward end portion of said electrodefor increasing the area for dissipating heat from the electrode and forincreasing mechanical strength of the forward end portion of saidelectrode, a main bulkhead provided at right angles to the longitudinaldirection of the indented or grooved portion along the axis of saidelectrode, said main bulkhead being connected to a convex surface of theindented or grooved portion, sub-bulkheads provided at both sides of themain bulkhead, said sub-bulkheads being connected to the convex surfaceof the indented or grooved portion in the longitudinal directionthereof, these main bulkhead and sub-bulkheads forming together a snakycooling liquid passage, one end of said snaky cooling passage beingconnected to the cooling liquid inlet passage and the other end of saidpassage being connected to the cooling liquid outlet passage,respectively, and covering plates covering portions surrounded by themain bulkhead, the sub-bulkheads and the inside wall of the anode exceptthe cooling liquid inlet and outlet passage portions so as to providespaces of suitable size therein.

1. A high pressure discharge lamp of the cooled electrode typecomprising electrodes, an envelope, sealing portions for said electrodesand said envelope, a cooling liquid inlet passage and a cooling liquidoutlet passage formed in the interior of at least one of said electrodesfor introducing a cooling liquid into the forward end portion of saidelectrode and discharging same therefrom, an indented or grooved portionprovided in the interior of the forward end portion of said electrodefor increasing the area for dissipating heat from the electrode and forincreasing mechanical strength of the forward end portion of saidelectrode, a main bulkhead provided at right angles to the longitudinaldirection of the indented or grooved portion along the axis of saidelectrode, said main bulkhead being connected to a convex surface of theindented or grooved portion, subbulkheads provided at both sides of themain bulkhead, said subbulkheads being connected to the convex surfaceof the indented or grooved portion in the longitudinal directionthereof, these main bulkhead and sub-bulkheads forming together a snakycooling liquid passage, one end of said snaky cooling passage beingconnected to the cooling liquid inlet passage and the other end of saidpassagE being connected to the cooling liquid outlet passage,respectively, and covering plates covering portions surrounded by themain bulkhead, the sub-bulkheads and the inside wall of the anode exceptthe cooling liquid inlet and outlet passage portions so as to providespaces of suitable size therein.